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Techniques and Methods 10–C5

Determination of the δ15N and δ13C of Total Nitrogen and Carbon in Solids; RSIL Lab Code 1832

By Kinga Révész, Haiping Qi, and Tyler B. Coplen

Thumbnail of and link to report PDF (512 KB)Summary

The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 1832 is to determine the δ(15N/14N), abbreviated as δ15N, and the δ(13C/12C), abbreviated as δ13C, of total nitrogen and carbon in a solid sample. A Carlo Erba NC 2500 elemental analyzer (EA) is used to convert total nitrogen and carbon in a solid sample into N2 and CO2 gas. The EA is connected to a continuous flow isotope-ratio mass spectrometer (CF-IRMS), which determines the relative difference in stable nitrogen isotope-amount ratio (15N/14N) of the product N2 gas and the relative difference in stable carbon isotope-amount ratio (13C/12C) of the product CO2 gas. The combustion is quantitative; no isotopic fractionation is involved. Samples are placed in tin capsules and loaded into a Costech Zero Blank Autosampler on the EA. Under computer control, samples then are dropped into a heated reaction tube that contains an oxidant, where combustion takes place in a helium atmosphere containing an excess of oxygen gas. Combustion products are transported by a helium carrier through a reduction furnace to remove excess oxygen and to convert all nitrous oxides into N2 and through a drying tube to remove water. The gas-phase products, mainly CO2 and N2, are separated by a gas chromatograph. The gas is then introduced into the IRMS through a Finnigan MAT (now Thermo Scientific) ConFlo II interface. The Finnigan MAT ConFlo II interface is used for introducing not only sample into the IRMS but also N2 and CO2 reference gases and helium for sample dilution. The flash combustion is quantitative; no isotopic fractionation is involved. The IRMS is a Thermo Scientific Delta V CF-IRMS. It has a universal triple collector, two wide cups with a narrow cup in the middle; it is capable of measuring mass/charge (m/z) 28, 29, 30 or with a magnet current change 44, 45, 46, simultaneously. The ion beams from these m/z values are as follows: m/z 28 = N2 = 14N14N; m/z 29 = N2 = 14N15N primarily; m/z 30 = NO = 14N16O primarily, which is a sign of contamination or incomplete reduction; m/z 44 = CO2 = 12C16O16O; m/z 45 = CO2 = 13C16O16O primarily; and m/z 46 = CO2 = 12C16O18O primarily.

Revised September 17, 2012 (version 1.2)

First posted 2006 and revised 2007

For additional information contact:
Director, Reston Stable Isotope Laboratory
U.S. Geological Survey
12201 Sunrise Valley Drive, MS 431
Reston, VA 20192
http://isotopes.usgs.gov/

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Suggested citation:

Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ15N and δ13C of total nitrogen and carbon in solids; RSIL lab code 1832, chap. 5 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 31 p., available only at http://pubs.usgs.gov/tm/2006/tm10c5/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)


Contents

Foreword

Summary of Procedure

Reporting Units and Operational Range

Reference Materials and Documentation

Labware, Instrumentation, and Reagents

Sample Collection, Preparation, Analysis, Retention Times, and Disposal

Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance

Health, Safety, and Waste-Disposal Information

Revision History

References Cited

Appendix A. Step-by-Step Procedure to Log-In Samples to LIMS-LSI

Appendix B. Step-by-Step Procedure to Create an Excel Sample-List Workbook and Print a Sample List

Appendix C. Step-by-Step Procedure for Weighing and Storing Samples

Appendix D. Step-by-Step Procedure of Zero Blank Autosampler Operation

Appendix E. Step-by-Step Procedure to Add Sample Information to Sequence Table

Appendix F. Step-by-Step Procedure to Retrieve Data from ISODAT 2.0 for LIMS-LSI and for Data Back-Up

Appendix G. Step-by-Step Procedure to Transfer Data to LIMS-LSI, to Transfer Data to Back-Up Computer, and to Reevaluate Old Data

Appendix H. Step-by-Step Procedure to Determine and Apply Correction Factors and Evaluate Data

Appendix I. Step-by-Step Procedure to Check Elemental Analyzer for Leaks

Appendix J. Daily Checklist

Appendix K. Changing the Insertion Tube

Appendix L. Changing the Water Trap

Appendix M. Changing the Reaction Tube

Appendix N. Step-by-Step Procedure to Report Data


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